I currently have a CoreDuo 15" MBP and acquired a Canon HD Camcorder. When I transfer the video to iMovie, it strongly recommends import at a lower resolution. Here is what iMovie's help file says:

"When you import 1080i-format video into iMovie you have the option of importing it at its full size and quality, or importing it at the "large" size, with dimensions of 960 by 540 pixels.
...
If you have a MacBook, MacBook Pro, or Mac mini computer, you may also find that importing the large size video plays back more smoothly in iMovie. It's true that the large size video does not preserve the quality of the full size video, but generally, the loss in quality is minor and not noticeable when used in the ways listed above."

I am considering getting the Penryn 17" with the screen upgrade (when this mythical beast appears...). Do the current 17" MBP with screen upgrade do well with 1080i? If not, is it anticipated that the Penryn model will? I realize that this is dependent on more than the screen, probably mainly video ram.

You'll be fine editing the video at the full resolution with the new macbook pro, whenever it comes out. I edited footage from the Sony FX1 which is also 1080i, using iMovie and it was fine. Sure the lower resolution will provide faster editing, but you'll be able to deal with full.

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